A power kite or traction kite is a relatively large foil-type kite intended to provide a pulling force to the user. Traction kites can be used to sail upwind under the same principles as used by other sailing craft. Several kite sailing sports have become popular, such as kite buggying, kite landboarding, kite boating, kite surfing and snow kiting. Traction kites used in water sports typically have inflatable leading edges or supported leading edges, so that they do not sink or collapse on contact with the water.
In use, traction kites generally need to be continuously manipulated by the user in order to control the flying trajectory of the kite to generate the required traction, to handle wind gusts and to keep the kite from descending to the ground.
For smaller crafts, like buggies, surfboards and dinghies, a traction kite can generally be controlled by hand. One common way of manipulating a traction kite is by means of a 3-point control system, where one centrally placed “power” line bears the main load of the kite, and two control lines are manipulated to sheet in and sheet out the flexible left and right tips of the kite. In a common kite setup, the centrally placed line branches out towards the kite to multiple connection points at the leading edge of the kite. The other end of the centrally placed line attaches to a structural part of the craft, or, in the case of surf-style kiting where the rider stands on a wheeled or sliding board, the centrally placed, load bearing line attaches to a fixed point (e.g., a spreader hook) on a harness worn by the rider, and the two control lines attach to the ends of a control bar located so as to be manipulable by a rider wearing the harness. In this arrangement, the force generated by the kite is applied to the harness worn by the rider.
The control bar used to steer and sheet the kite often features a central hole through which the central load bearing line passes. By moving the control bar along the load bearing line in a direction away from the fixed point on the rider's harness, the tips of the kite are “sheeted” out, spilling wind from the kite. By sliding the moving the bar towards the fixed point on the rider's harness, the tips of the kite are sheeted in, causing the kite to spill less wind and thus to “power up”. Pulling one end of the control bar more than the other end will cause the kite to sheet in on the side pulled in, and to sheet out on the other side, causing the kite to tend to turn about the sheeted in side.
The range of movement of the control bar along the central load bearing line is limited by the assembly that attaches to the rider's harness, typically a loop of strong line covered in PU tubing that hooks onto a spreader bar/hook assembly mounted on the front of the rider's harness. This spreader bar/hook assembly is the primary power/force load point between the rider and the kite. The rider's arms and hands are primarily used to provide control turn input into the kite control bar so as to provide turn and sheeting input to the kite, and generally are subjected to only a relatively small portion of the pulling force imparted by the kite.
It is desirable for the harnesses worn by kite riders to be strong, comfortable and securely fitted, to enable proper control of the kite. Typically, such harnesses includes a generally flexible waist belt (or waist band) secured about the rider and are configured such that a generally rigid spreader bar/hook assembly may be attached to the harness at the rider's front.
For comfort (primarily in terms of spreading loads on the rider's body), harnesses typically have foam padding and reinforcing in the form of strong fabrics and webbing. Known harnesses have several different fitting and tightening adjustment means. A common adjustment means for a waist belt is an overlapping wrap closure at the harness front, with the overlapping ends of the waist belt secured one to the other with a conventional hook and loop fastener (e.g., Velcro™). Locating the overlapping ends of the waist belt at the rider's front provides desirable extra padding and chafe protection between the rider and the spreader bar/hook assembly.
In use, the spreader bar/hook assembly extends across the front of the harness and each end of the spreader bar/hook assembly is attached to the harness in the vicinity of a respective hip of the rider, by an attachment means that generally permits some adjustment of the relative positions of the spreader bar/hook assembly and the harness, so as to accommodate physical differences between riders and differences in the other components of the kite assembly. The spreader bar is typically about 12″ long and is intended to provide a comfortable load angle for the forces of the kite to be transferred to the hips of the rider.
The attachment means between the spreader bar/hook assembly and the harness may comprise webbing passing through an opening in the spreader bar and suitable securing means (such as buckles) and/or purpose-designed clips. In some harnesses, additional support for the spreader bar is provided by various support straps to secure and position the spreader bar, however these straps tend to increase the time required for a rider to put on and remove the harness.
The spreader hook is the point of connection between the harness and the power line of the kite. The power line of the kite is hooked to the spreader bar via the “trim loop”. The spreader hook is made from a relatively strong material or materials, such as stainless steel or a suitable plastic. The actual hook used to connect with the trim loop typically protrudes out from the bar 2 to 3 inches and is in a C shape.
There are several methods to don a harness. Some riders loosen side buckles to release tension on the webbing, including webbing securing the spreader bar to the harness, which allows the rider to slide the harness over their legs and up to their waist. Some spreader bars feature clips or hook systems that enable the rider to disconnect the bar, however the webbing used to hold the harness secure must still be loosened before the latch or hook can be opened allowing the doff or don process.
It is common for a harness to include a grab handle, being a strong webbing handle, typically located at the back of the harness, which can be used by an assistant to help stabilize the rider while launching or landing a kite. Kite boarding instructors also use grab handles to stabilize students during lessons.
Use of propulsive wings and traction kites involves a number of risks. Pilot error as well as defects in material and design, can result in serious injuries and even death, as the forces produced by a kite can be significant. Loss of control of a kite by a rider and an associated inability of the rider to depower the kite, have resulted in very serious injuries and fatalities, including as caused by failures in the control bar and kite systems, lines tangling with the harness, partial immersion of harnesses at speeds resulting in the harness scooping water (referred to as bucketing), etc.
Efforts have been made in the kite board industry to improve the safety of the kite control bars and kites, and to provide means to reduce the power of the kite in an emergency. For example, responsive to the danger of line tangles, many kite-specific harnesses come fitted with a safety knife attached to the harness in an easy to reach location.
Further, many harnesses and kite assemblies include means for releasing the power line from the spreader hook.
The configuration of the spreader hook is important to the proper operation of kite release systems, as most such systems rely on a means for opening the trim loop so as to enable it to slide through the spreader hook. However, there have been serious accidents and fatalities due to the loops becoming jammed in the spreader hook when released, leaving the rider with no way to disengage from the power of the kite or to depower the kite. Alternate/backup configurations include spreader bars with hinging or releasing hooks that free the trim loop from the harness without opening the trim loop.
As a released kite poses potential danger to others downwind, to avoid losing a released kite, with such kite release means, it is standard practice to use a separate safety leash attached between the kite and a location on the harness separate from the spreader hook. With such leashes, to minimize the pulling force of the kite on the rider, it is desirable that a depowering action be activated at the kite when the leash is loaded by tension between the kite and the harness.
It is not uncommon for riders to attach the kite leash to the grab handle. Some harnesses also feature a handle pass leash attachment line that runs across the back of the harness. Kite safety leashes are attached to these back locations to allow ease of certain maneuvers such as handle passes. However, when a released kite loads a kite leash attached to the back of a harness, it can spin the rider facing backwards, making it difficult or impossible to reach a safety release for the leash. As well, the harness of a rider being dragged backwards through the water by a leash, may bucket, that is, scoop water, resulting in greater drag resistance (and thus greater tension on the leash and less depowering effect on the kite) and possibly a tendency to submerge the rider. There have been injuries and fatalities related to riders being dragged by their kite leashes being unable to reach their kite leash release.
In some cases, the kite leash may be attached to the side of a harness or to the spreader bar (typically to a loop affixed to the spreader bar). Although such attachment locations avoid some of the potential problems associated with attaching a leash at the back of a harness, at times a kite and the associated lines can tangle during a release, making the desired depowering effect of the kite release system ineffective. Even a kite leash attached to the front of the harness within easy reach of the rider can become tangled, making it impossible for the rider to release or depower the kite, resulting in a potentially dangerous high-speed drag or lofting, and possibly undesirable bucketing.